Efficient Production of High-energy Nonthermal Particles during Magnetic Reconnection in a Magnetically Dominated Ion-Electron Plasma

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Astrophysical Journal Letters






Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux-dominated flows. In this Letter, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically dominated ion-electron plasma using fully kinetic simulations. For an ion-electron plasma with a total magnetization of σ0 = B2/(4πn(mi + me)c2), the magnetization for each species is σi ∼ σ0 and σe ∼ (mi/me)σ0, respectively. We have studied the magnetically dominated regime by varying σe = 103-105 with initial ion and electron temperatures Ti = Te = 5 - 20mec2 and mass ratio mi/me = 1 - 1836. The results demonstrate that reconnection quickly establishes power-law energy distributions for both electrons and ions within several (2-3) light-crossing times. For the cases with periodic boundary conditions, the power-law index is 1 > s > 2 for both electrons and ions. The hard spectra limit the power-law energies for electrons and ions to be γbe ∼ σe and γbi ∼ σi, respectively. The main acceleration mechanism is a Fermi-like acceleration through the drift motions of charged particles. When comparing the spectra for electrons and ions in momentum space, the spectral indices sp are identical as predicted in Fermi acceleration. We also find that the bulk flow can carry a significant amount of energy during the simulations. We discuss the implication of this study in the context of Poynting-flux dominated jets and pulsar winds, especially the applications for explaining nonthermal high-energy emissions. © 2016. The American Astronomical Society. All rights reserved.


acceleration of particles - galaxies; general - magnetic reconnection - pulsars; general - relativistic processes; jets - gamma-ray burst



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